1. Field of the Invention
The present invention relates to a method of ejecting liquid droplets and an apparatus for ejecting liquid droplets in fixed amount, in which a liquid under regulated pressure is ejected while it is caused to fly in the form of liquid droplets from a valve ejection port. More particularly, the present invention relates to a method of ejecting liquid droplets and an apparatus for ejecting liquid droplets in fixed amount, which are suitably used to handle various kinds of liquids including a solution having a uniform concentration, a liquid containing fillers, liquids having any viscosity from a low to high level, and a highly-viscose paste-like liquid as a combination of those liquids.
2. Description of the Related Art
In a conventional apparatus for ejecting liquid droplets, a liquid material supplied to a valve body is pushed into a flow passage within the valve body under constant pressure regulated by a pressure regulating device. However, such a conventional apparatus has a problem as follows. When a valve is opened, i.e., when a plunger rod is retracted to move away from a valve seat, air is sucked through an ejection port formed at a nozzle end, and bubbles are mixed in the liquid inside the valve body. As a result, the liquid cannot be ejected in desired amount.
The inventor has found that the above-mentioned phenomenon occurs for the reason given below. When the plunger rod is shifted from a valve-closed state in which the rod is seated against the valve seat provided in the valve body, to a valve-open state in which the rod is retracted to move away from the valve seat, a volume that is occupied by the plunger rod in the flow passage within the valve body is reduced and the pressure in the flow passage is lowered correspondingly. This causes a pressure difference between the nozzle end and the flow passage, and the pressure difference increases as the shift speed of the plunger rod is increased. Therefore, the supply amount of the liquid material pushed into the flow passage within the valve body under a constant pressing force cannot follow the pressure difference, thus resulting in a phenomenon that the atmosphere is sucked into the flow passage through the ejection port formed at the valve end for evenness of pressure. Particularly when the liquid is continuously ejected at a high-speed tact (short cycle), such a phenomenon appears noticeably because the plunger rod must be contracted at high speed.